The present invention relates to a self-locking differential gear for motor vehicles; such differentials are sometimes referred to as limited-slip differentials. Known such differential gears include a housing which is rotatable with respect to the chassis or body of the motor vehicle and which is driven via a transmission shaft from the engine of the vehicle. The housing has two output shafts which are coaxially aligned with one another, their respective inner ends, within the housing, facing one another but being spaced a certain distance apart: these output shafts are connected directly to the corresponding half shafts which transmit drive to the driving wheels of the motor vehicle. Between the housing and the two output shafts is a kinematic connection means which usually includes a pair of coaxial conical gear wheels respectively connected to the two output shafts of the differential gear, and at least two intermediate conical gear wheels serving as satelite gears between the two main conical gears mentioned above; these conical satelite gears are supported by pins rigidly on the closed housing of the differential gear.
The self-locking feature of prior art differential gears is obtained by means of auxiliary elements rigidly connected to the two output shafts and provided with friction surfaces which become pressed against corresponding friction surfaces formed on the housing or on elements carried by the housing, by the action of resilient means. In this way, relative sliding movement which takes place between the frictional surfaces mentioned above in certain operating conditions, that is when the output shafts rotate with respect to the housing, causes a resistive couple to be formed which permits the transmission of a certain twisting moment to one of the two half shafts even in a case in which the other of the two half shafts is rotating freely due to skidding or slipping of the associated road wheel of the motor vehicle. This type of differential gear is, however, of a notably complex construction and is therefore also rather costly, requiring for its construction the use of elements such as gears and springs which necessitate, for their manufacture, the use of rather sophisticated technology.